Hitherto, as for cam operation, a mechanical cam for providing output in conjunction with motion of a cam attached to a shaft has been used. In a method using the mechanical cam, it is difficult to adjust a cam pattern. Thus, an electronic cam has been used for which the relationship between rotation of a shaft and cam shape data is previously registered, the rotation position of the shaft is detected, and based on the detection value, a servomotor is controlled for performing cam operation.
In such electronic cam control, a servo control system disclosed in JP-A-7-104855 is available for the purpose of decreasing the difference between a position command and position feedback. In an electronic cam phase control method for controlling a servo system in accordance with a position command having a predefined position pattern relative to the transition of a phase command θ, the servo control system generates a phase delay amount Δθ caused by a follow-up delay of the servo system relative to the position command as a function of phase transition speed ω, inputs a signal with the phase delay amount Δθ added to the phase command to a position pattern generation circuit, and adopts an output signal therefrom as a position command of the servo system.
Such a servo control system can compensate for the phase delay of the electronic cam.
However, the above-described servo control system outputs the position command in advance almost proportional to the phase delay amount and thus compensates only for the phase delay amount. That is, it does not compensate for the follow-up delay of the servo system and thus particularly if the control speed is high, the follow-up delay of the servo system becomes noticeable as shown in FIG. 7. Thus, the locus of the actual positions of the servomotor differs largely from the locus of the position command prepared from a cam pattern and the actual position difference between the position command and the servomotor becomes ΔL at time ta; this is a problem.